Engineer arrested over Bangladesh building collapse

Police investigating the collapse of a Bangladesh factory building that killed more than 500 people have arrested an engineer who warned that the complex was unsafe.

The arrest of engineer Adbur Razzak brought to nine the number of people held over the April 24 disaster, which has put a spotlight on many Western clothing retailers who use Bangladesh as a source of cheap goods.

One firm whose garments were being made in the doomed eight-storey building, Canada's Loblaw, said it would continue to produce clothes in Bangladesh but promised to improve the facilities it uses there.

The death toll from Bangladesh's worst industrial accident rose to 501 on Friday, with scores of relatives still gathered at the site in a Dhaka suburb clutching photographs of loved ones attesting to the many more still missing.

Razzak had been called to Rana Plaza in Savar, 20 kilometres north of the capital, by its owner when cracks appeared in concrete pillars the day before the accident.

Despite his warning that the building was unsafe - quoted in local media hours before it came crashing to the ground - thousands of mostly female workers were sent back into its upper-storey factories when the morning shift began the next day.

Police said Razzak had been arrested because he had been involved in the original construction of the building.

Duty-free access offered by Western countries and low wages have helped turn Bangladesh's garment exports into a $19 billion-a-year industry, with 60 per cent of clothes going to Europe.

The European Union had said it was considering trade action against Bangladesh, which has preferential access to EU markets for its garments, to pressure Dhaka to improve safety standards.

Human rights groups say there has never been a case in which a factory owner was prosecuted over the deaths of workers.